UIImage *aimage = [UIImage imageNamed:@"xxx"];
UIImage *image = [aimage imageWithRenderingMode:UIImageRenderingModeAlwaysOriginal];
UIBarButtonItem *rightItem = [[UIBarButtonItem alloc] initWithImage:image style:UIBarButtonItemStylePlain target:self action:@selector(action_rightClick:)];
[self.navigationItem setRightBarButtonItem:rightItem animated:YES];
图片尺寸要标准的44 ＊ 44，或40 ＊ 40
